On the 1000th day since the launch of the first module of the International Space Station, Discovery's astronauts were awakened shortly after 4 a.m. Central time to the sounds of "The Marvelous Toy" by Tom Paxton for Mission Specialist Dan Barry from his wife.

Barry and crewmate Pat Forrester will conduct the first space walk of Discovery's flight to the International Space Station at around 9:30 this morning to install the Early Ammonia Servicer on the station's P6 truss structure. The servicing unit contains spare ammonia that could be used in the station's cooling system, if needed.

They also will attach an experiment to the station to expose samples of materials to the space environment. Carrying the acronym MISSE, for Materials International Space Station Experiment, it contains about 1,500 samples of materials in two suitcase-like containers. The samples will remain outside the station for about a year, then will be returned to Earth for analysis.

Discovery Commander Scott Horowitz will operate the shuttle's robotic arm during the space walk. Pilot Rick Sturckow will serve as the space walk choreographer from inside the shuttle's cabin during the 61/2-hour space walk, which will be staged from Discovery's airlock.

A second space walk is planned for Saturday. Barry and Forrester will hook up heater cables for another truss structure to be delivered to the station next year.

Aboard the ISS, the computers of the Zvezda Service Module once again commanded the station's gyroscopes to assume control of the orientation of the complex at around 5 a.m. after Russian flight controllers completed their loading of upgraded software commands to those computers. In the meantime, Discovery maintained control of the complex until the computer upgrades were completed with no impact to station operations.

While Barry and Forrester conduct their space walk, the Expedition Three crew, Commander Frank Culbertson, Pilot Vladimir Dezhurov and Flight Engineer Mikhail Tyurin, will continue stowage of equipment and supplies inside the Leonardo Multi-Purpose Logistics Module for return to Earth. The Italian-built pressurized module brought almost 7,000 pounds of equipment, supplies and two scientific experiment racks to the station.

At 7:10 this morning, Culbertson and his crewmates plan to offer a few commemorative words to mark the 1000th day in space for the International Space Station since the Zarya module was launched on November 20, 1998 from the Baikonur Cosmodrome in Kazakhstan.

Discovery and the station are orbiting the Earth every 90 minutes at an average altitude of 244 statute miles with all systems functioning normally.